A semiconductor laser typically comprises a substrate, a first clad layer overlying a surface of the substrate, an active region overlying the first clad layer and a second clad layer overlying the active region and a pair of parallel reflecting end faces between which the laser oscillation occurs. This structure provides optical confinement in the transverse direction, the direction perpendicular to the plane of the active region and to the direction of laser oscillation. In the lateral direction, the direction in the plane of the active region and perpendicular to the direction of laser oscillation, it has been found useful to introduce a non-planar structure into the substrate in order to form a refractive index optical waveguide in the lateral direction. The non-planar structure may be a rectangular, dovetail or V-shaped channel in the substrate's surface which extends between the end faces. Laser action then occurs in the active region over the channel with the laterally varying distance between the higher refractive index substrate and the active region providing the refractive index guide. Such structures have been shown to produce moderate output power, on the order of 20 milliwatts, in the fundamental spatial, lateral and transverse, mode.
However, the deposition of the layers over the channel in the substrate results in irregularities such as terraces in the surfaces of these layers which in turn produce kinks in the comparatively thin active layer over the channel. These irregularities produce non-uniformities in the refractive index guide which affect the threshold, the lasing action and the mode structure of the output laser beam, thereby limiting the maximum power attainable from the laser and also the manufacturing yield. Burnham et al. in U.S. Pat. No. 4,317,085 and others have identified these irregularities as arising from differing liquid phase epitaxy growth rates on the different faces of the channel. Burnham et al. disclosed that these irregularities could be reduced or eliminated by depositing the layers over a substrate mesa with the channel therein. This approach, however, requires two separate masking and etching steps, both of which must be carefully controlled to produce the desired result. Thus, it would be desirable to have a structure which substantially eliminated these growth-induced irregularities without the necessity of using the two step etching process.